Plate heat exchangers for three heat exchanging fluids have many potential fields of application. They may for example be used as evaporators for evaporation of refrigerants flowing in refrigeration systems. Such a refrigeration system normally includes a compressor, a condenser, an expansion valve and an evaporator. A plate heat exchanger used as an evaporator in a system of this kind often has heat exchanging plates that are welded or brazed together, but also packings may be used for sealing between the heat transferring plates.
U.S. Pat. No. 5,462,113 shows a plate heat exchanger with flow passages for three different fluids between the plates. The delivery of the three fluids to the core of plates is done in such a way that passages for the number one fluid are present on both sides of every passage for each one of the two remaining fluids. In a preferred embodiment the passages are created using two different kinds of plates. Good sealing between adjacent plates at the openings creating the inlet and outlet channels for the three fluids is created by designing the areas around the ports thereby defining a system with annular planar plateaus.
The design of the heat exchanger for three heat exchanging fluids gives the possibility of flexible operational solutions in connection with part load. The heat transfer is however not maximal effective.